1. Field of the Invention
This invention relates generally to miniature rotary machinery with brushgear, and more particularly to miniature rotary machinery with brushgear comprising two sets of brush arms having brushes at one end thereof, and brush arm eyes, for rotatably engaging with arm guides, to which power supply voltage is fed, at the other end thereof so as to ensure stable electrical contact between the brush arm eyes and the arm guides.
2. Description of the Prior Art
The conventional type of brushgear for use in permanentmagnet field type high-power miniature rotary machinery, a miniature motor, for example, usually has such a construction that brushes and a spring are incorporated in a cylindrical brush holder to push the brushes by the resiliency of the spring. The brushgear of this construction, however, has a drawback in that the pushing force of the brushes tends to change with the wear of the brushes, leading to unstable pushing force. Furthermore, the conventional type of brushgear tends to be of a complex construction. Another conventional type of brushgear has such a construction that brushes are installed on brush arms, made of a resilient material, and auxiliary brush arms are provided to reinforce the insufficient pushing force of the brushes in the aforementioned conventional type of brushgear. The brushgear of this construction also has drawbacks in that the pushing force of the brushes tends to be unstable due to the wear of the brushes, the construction is complicated, and the brushes cannot be replaced easily. To solve these problems, the present Applicant previously filed a patent application (Utility Model Application No. 120850/1984) in Japan. In the following, miniature rotary machinery with brushgear as claimed in the previous application will be described, referring to FIGS. 2 through 6.
In FIG. 2 illustrating a perspective view of the miniature rotary machinery according to the previous application and FIG. 3 showing a longitudinal section of the same, a housing 2 and a case cover 3 are fixedly fitted to both ends of a cylindrical motor case 1 with fastening screws 4. Slotted holes (not shown) for the fastening screws 4 are provided on the housing 2 so that the mounting position of the case cover 3 on the motor case 1 can be changed to position brushes at the optimum commutating positions in accordance with the rotating direction of the motor, as will be described later. The slotted holes function as coolling vent holes, together with vent holes (not shown). The central part each of the housing 2 and the case cover 3 pivotally supports a shaft 9 of a rotor 8 by means of bearings 7. A commutator 10 is fixedly fitted to the shaft 9 on the side of the case cover 3. A plurality of vent slots 11 for dissipating the heat generated by the rotor 8, etc. are provided at appropriate intervals on the case cover 3 above the commutator 10. A substantial part on the bottom of the case cover 3 is cut away, except a rim part 3a on which brushgear 12, which will be described later, is installed. On the cut-away part on the bottom of the case cover 3, that is, on the inside surface of the case cover 3, mounted is the brushgear 12. Two magnets 13 are mounted at the central part of the motor case 1. The magnets 13 are indicated at the top and bottom positions in FIG. 3 by turning 90 degrees from the actual mounting positions thereof for the sake of clarity. Needless to say, these magnets 13 do not interfere with the screws 4 in the actually assembled state.
Next, the brushgear 12 will be described in the following. As is apparent from FIGS. 3, 4 (front view), 5 (righthand side elevation), 6 (A) (enlarged sectional view of the brush arm) and 6 (B) (enlarged view of the brush arm in another embodiment), two arm guides 14 are fixedly fitted to the rim part 3a of the case cover 3. The aforementioned case cover 3 is made of an insulating material, such as synthetic resin, and is fixedly fitted via washers 15 to the arm guides 14, made of a metallic material, by staking and other methods. A post supporting base 16a provided at one end of the brush arm 16, which is formed into a columnar shape having a diameter equal to the diameter of the post of the arm guide 14, is engaged with each arm guide 14. A terminal plate 17, which is electrically connected to the end face 16b of the brush arm 16, is also engaged with each arm guide 14. The terminal plate 17 is fixed to each arm guide 14 via a fixing plate 18, made of an insulating material, with a screw 19. To reinforce the brush arm 16, a rib 16c is provided at the post supporting base 16a of the brush arm 16, and a bent piece 16d is formed on the longitudinal side surface of the brush arm 16. As a means to ensure good electrical contact between the arm guide 14 and the brush arm 16, a plurality of ridges 16e, for example, may be formed on the inside surface of the brush arm 16 so as to bring the brush arm 16 in close contact with the outside surface of the arm guide 14, as shown in FIG. 6 (B).
A brush 20 is provided at the tip of the brush arm 16, and a spring receptacle 21, made of an insulating material, is provided at the central part of the brush arm 16. As shown in FIG. 4, each end of a metallic spring 22, which is formed into an arc shape to obtain resiliency, is engaged with each of the spring receptacles 21 provided on the two brush arm 16. When considering the mechanical action of the metallic leaf spring 22 of such a construction, each brush arm 16 is pushed in the lateral direction by the resiliency of the metallic leaf spring 22, and thus pushing force is imparted to the brush 20 by the rotating moment generated around the post supporting base 16a of the brush arm 16 engaged with each arm guide 14. The displacement of the brush arm 16 caused by the metallic leaf spring 22, when the brush 20 is worn out, would be considerably smaller than the displacement of the tip of the brush arm 16 due to the wear of the brush 20. Consequently, the resiliency of the metallic leaf spring 22 even after the wear of the brushes, would be almost equal to the resiliency thereof before the wear of the brush 20, and the aforementioned rotating moment around the post supporting base 16a of the brush arm 16 can be considered virtually the same. This means that the pushing force exerted by the brush on the commutator 10 is kept always constant, independently on the wear of the brush 20.
When considering the electrical performance of the metallic leaf spring 22, the brush arms are doubly insulated at two locations by the spring receptacles 21, made of an insulating material, provided on the brush arms 16. Consequently, should either of the brush arms 16 make electrical contact with the metallic leaf spring 22 by mistake, insulation is maintained by either of the spring receptacles 21, and no shortcircuiting takes place between the two brush arms 16.
When replacing the brushes 20, both ends of the arcshaped metallic leaf spring 22 are disengaged from the spring receptacles 21. And then, the brush arm 16 can be easily removed by loosening each fastening screw 19 fastening the brush arm 16 and the terminal plate 17, and sliding the brush arm 16 sideways from the arm guide 14 from the left to the right in FIG. 3. Thus, the brush 20 can be easily replaced by replacing the brush 20 on the removed brush arm 16 with a new one, or installing the pre-assembled brush/brush arm unit in the reverse order.
Since the brushgear 12 described above is installed on the side of the lower inside surface of the case cover 3, the brush 20 is rotated together with the case cover 3 as the case 3 is rotated. Therefore, the relative positions of the brushes 20 with respect to the magnet 13 installed on the housing 2 can be adjusted by moving the fixing position of the case cover 3 by shifting the locations of the fastening screws 4 along the slotted holes 5 on the housing 2. Thus, the brushes 20 can be easily moved to the optimum commutating positions in accordance with the rotating direction of the motor.
In the foregoing, the miniature rotary machinery with brushgear which was filled by the present Applicant has been described. To improve electrical connection between the brush arm and the arm guide, the present Applicant filed in Japan another patent application, Utility Model Application No. 176146/19184 (hereinafter referred to as the second application). In the following, the second application will be described, referring to FIG. 7, which is an enlarged sectional view of the portion at which the brush arm is fixedly fitted to the arm guide in miniature rotary machinery using the brushgear of the second application.
Miniature rotary machinery with the brushgear of the second application has essentially the same construction as the first application described earlier with reference to FIGS. 2 through 6, except that a ring-shaped projection 14a is provided on the side surface of the arm guide 14, as shown in FIG. 7.
In miniature rotary machinery having the brushgear embodying the aforementioned first or second applications, the radius of the brush arm eye portion at which the brush arm eye comes in contact with the arm guide is made slightly larger because of the need to make the brush arm rotatable with respect to the arm guide. This inevitably leads to a certain degree of play between the brush arm and the arm guide. The aforementioned first and second applications therefore involve an unwanted problem of the play deteriorating electrical connection between the brush arm and the arm guide.